Detachable, varying flexibility, aneurysm neck bridge

ABSTRACT

This is a device for bridging the neck of either a wide-necked or narrow-necked aneurysm as may be found in the vasculature. It may be used to stabilize the placement of vaso-occlusive devices such as helically wound coils in the aneurysm or may be used to, at least partially, close the aneurysm neck. The vaso-occlusive devices, commonly helically wound coils, are delivered by a core wire which is linked to the coils by an electrolytically severable joint. The core wire will often be insulated. The retainer assembly itself is also attached to another delivery device, such as a core wire, and desirably is severed from the core or delivery wire by the use of another electrolytically severable joint. The inventive neck bridge typically has a number of array elements which are intended to be resident within the aneurysm after the device is deployed from the distal end of a catheter. Central to this invention is the use of array elements having differing flexibility or constituent members of the array elements, e.g., wires making up the array elements, which are of differing flexibilities. After deployment of this retainer, the aneurysm may be at least partially filled with vaso-occlusive devices such as helically wound coils.

FIELD OF THE INVENTION

This invention is a device for bridging the neck of either a wide-neckedor narrow-necked aneurysm as may be found in the vasculature. It may beused to stabilize the placement of vaso-occlusive devices such ashelically wound coils in the aneurysm or may be used to, at leastpartially, close the aneurysm neck. The vaso-occlusive devices, commonlyhelically wound coils, are delivered by a core wire which is linked tothe coils by an electrolytically severable joint. The core wire willoften be insulated. The retainer assembly itself is also attached toanother delivery device, such as a core wire, and desirably is severedfrom the core or delivery wire by the use of another electrolyticallyseverable joint. The inventive neck bridge typically has a number ofarray elements which are intended to be resident within the aneurysmafter the device is deployed from the distal end of a catheter. Centralto this invention is the use of array elements having differingflexibility or constituent members of the array elements, e.g., wiresmaking up the array elements, which are of differing flexibilities.After deployment of this retainer, the aneurysm may be at leastpartially filled with vaso-occlusive devices such as helically woundcoils.

BACKGROUND OF THE INVENTION

Different implantable medical devices have been developed for treating anumber of ailments associated with body lumens. In particular, occlusivedevices are useful in filling vascular or other body spaces. Some bodyspaces, such as vascular aneurysms, are formed due to a weakening in thewall of an artery. Often these aneurysms are the site of internalbleeding and, catastrophically, the site of strokes. A variety ofdifferent embolic agents are known as, at least arguably, suitable fortreatment of these openings. These treatments are commonly known as"artificial vaso-occlusion."

One such class of embolic agents includes injectable fluids orsuspensions, such as microfibrillar collagen, various polymeric beads,and polyvinylalcohol foam. These polymeric agents may additionally becrosslinked (sometimes in vivo) to extend the persistence of the agentat the vascular site. These agents are often introduced into thevasculature through a catheter. After such introduction, materials thereform a solid space-filling mass. Although some provide for excellentshort term occlusion, many are thought to allow vessel recanalizationdue to absorption of polymer into the blood. Another procedure in whicha partially hydrolyzed polyvinylacetate (PVA) is dissolved in an ethanolsolvent and injected into a desired vascular site is found in Park etal. (attorney docket no. 29025-20112.00) U.S. patent application Ser.No. 08/734,442, filed Oct. 17, 1996, for "LIQUID EMBOLIC AGENTS".

Other materials such as hog hair and suspensions of metal particles havealso been suggested and used by those wishing to form occlusions.

Other materials including polymer resins, typically cyanoacrylates, arealso employed as injectible vaso-occlusive materials. These resins aretypically mixed with a radio-opaque contrast material or are maderadio-opaque by the addition of a tantalum metal powder. Their use isfraught with problems in that placement of the mixture is quitedifficult. These materials are ones which crosslink with the human body.Inadvertent embolisms in normal vasculature (due to the inability ofcontrolling the destination of the resins) is not uncommon. The materialis also difficult or impossible to retrieve once it has been placed inthe vasculature.

Over the past few years, advancements in the artificial occlusions ofvessels and aneurysms have occurred due to the delivery and implantationof metal coils as vaso-occlusive devices. Implantable metal coils thatare useful as artificial occlusion devices in vasculature lumens oraneurysms are herein referred to as "vaso-occlusions coils."

Vaso-occlusive coils are generally constructed of a wire, usually madeof a metal or metal alloy, that is wound into a helix. Many such devicesare introduced in a stretched linear form to the selected target sitethrough a catheter. The vaso-occlusive device assumes an irregular shapeupon discharge of the device from the distal end of the catheter. Avariety of vaso-occlusive coils and braids are known. For instance, U.S.Pat. No. 4,994,069, to Ritchart et al., shows a flexible, preferablycoiled, wire for use in small vessel vaso-occlusion. Unlikevaso-occlusive coils used prior to that time, Ritchart taught a coilwhich is fairly soft and is delivered to the site using a pusher withina catheter lumen. Upon discharge from the delivery catheter, the coilmay undertake any of the number of random or regular configurations usedto fill the site. The coils are used for small vessel sites, e.g., 0.5-6mm in diameter. The coils themselves are described as being between0.010 and 0.030 inches in diameter. The length of the coil wire istypically 15 to 20 times the diameter of the vessel to be occluded. Thewire used to make up the coils may be, for instance, 0.002 to 0.006inches in diameter. Tungsten, platinum, and gold threads or wires aresaid to be preferred. These coils have a variety of benefits includingthe fact that they are relatively permanent, they may be easily imagedradiographically, they may be located at a well defined vessel site, andthey can be retrieved.

It is common that these vaso-occlusive devices be delivered throughmicrocatheters such as the type disclosed in U.S. Pat. No. 4,739,768, toEngelson. These microcatheters track a guidewire to a point justproximal or within the desired site for occlusion. The coil is advancedthrough the microcatheter (once the guidewire is removed) and out thedistal end hole so to at least partially fill the selected space andcreate an occlusion.

In addition to vaso-occlusion devices or coils having predeterminedsecondary shapes that dictate in part their space filling mechanism,other vaso-occlusive coils have been disclosed that take on randomshapes when expelled from a delivery sheath. One such type is avaso-occlusive coil often referred to as "a liquid coil". One example ofsuch a vaso-occlusive coil is disclosed in U.S. Pat. No. 5,690,666, toBerenstein et al. This patent describes a very soft and flexible coilwhich is flow-injectable through a delivery catheter using, e.g., salinesolution.

In addition to the various types of space-filling mechanisms andgeometries of vaso-occlusive coils, other particularized features ofcoil designs, such as mechanisms for delivering vaso-occlusive coilsthrough delivery catheters and implanting them in a desired occlusionsite, have also been described. The examples of categories ofvaso-occlusive coils based upon their delivery mechanisms includepushable coils, mechanically detachable coils, and electrolyticallydetachable coils.

One example of the type of vaso-occlusive coil referred to above as the"pushable coil" is disclosed in Ritchart et al., discussed above.Pushable coils are commonly provided in a cartridge and are pushed or"plunged" from the cartridge into a delivery catheter lumen. A pusheradvances the pushable coil through and out of the delivery catheterlumen and into the site for occlusion.

Mechanically detachable vaso-occlusive devices are typically integratedwith a pusher rod or wire and are mechanically detached from the distalend of that pusher after exiting a delivery catheter. Examples of suchmechanically detachable vaso-occlusive coils are found in U.S. Pat. No.5,261,916, to Engelson, or U.S. Pat. No. 5,250,071, to Palermo.

Finally, examples of electrolytically detachable vaso-occlusive devicesmay be found in U.S. Pat. Nos. 5,122,136 and 5,354,295, each toGuglielmi et al. In these devices, the vaso-occlusive portion of theassembly is attached to a pusher via a small electrolytically severablejoint. The electrolytically severable joint is severed by the placementof an appropriate voltage on the core wire. The joint erodes inpreference either to the vaso-occlusive device itself or to the pushercore wire. The core wire is often simply insulated to prevent theelectrolytic response caused by the imposition of electrical current.

Further improvement upon the electrolytical detachment mechanismdescribed just is found in U.S. Pat. Nos. 5,643,254 and 5,669,905, toScheldrup et al. These patents describe superimposing a modestalternating current upon the direct current signal. A sensing circuitmonitors the alternating current as an indicator of the progression ofcoil detachment.

Improvements in enhancing the thrombogenic or other occlusive tissueresponse to metal coils has also been disclosed. For example,vaso-occlusive coils having fibers attached thereto are known--see, forexample, U.S. Pat. No. 5,226,911, to Chee et al.

Each of the devices described above may be used in the treatment byocclusion of aneurysms. As noted above, aneurysms present particularlyacute medical risk due to the dangers of potential rupture of the thinwall inherent in such an aneurysm. Occlusion of aneurysms by the use ofvaso-occlusive coils without occluding the adjacent artery is a specialchallenge and is a desirable method of reducing such risk of rupture.

As noted above, the use of vaso-occlusive coils in treating aneurysms iswidespread. These vaso-occlusive devices are placed in an aneurysm inthe following fashion. A microcatheter is initially steered into oradjacent to the entrance of an aneurysm, typically aided by the use of asteerable guidewire. The wire is then withdrawn from the micro catheterlumen and replaced by the vaso-occlusive coil. The vaso-occlusive coilis advanced through and out of the microcatheter, desirably beingcompletely delivered into the aneurysm. After, or perhaps, during,delivery of such a coil into the aneurysm, there is a specific risk thata portion of the coil might migrate out of the aneurysm entrance zoneand into the feeding vessel. The presence of such a coil in that feedingvessel may cause the undesirable response of causing an occlusion there.Also, there is a quantifiable risk that the blood flow in the vessel andaneurysm may induce movement of the coil farther out of the aneurysm,resulting in a more developed embolus in the patent vessel.

One type of aneurysm, commonly known as a "wide neck aneurysm" is knownto present particular difficulty in the placement and retention ofvaso-occlusive coils. Wide neck aneurysms are herein referred to asaneurysms of vessel walls having a neck or a "entrance zone" from theadjacent vessel, which entrance zone has a diameter that either: (1) isat least 80% of the largest diameter of the aneurysm; or (2) isclinically observed to be too wide effectively to retain vaso-occlusivecoils that are deployed using the techniques discussed above.

Furthermore, vaso-occlusive coils lacking substantial secondary shapestrength may be difficult to maintain in position within an aneurysm nomatter how skillfully they are placed.

There are few disclosed devices for maintaining the presence ofvaso-occlusive coils within an aneurysm. One such device is shown inU.S. patent application Ser. No. 08/690,183, Kupiecki et al for"ANEURYSM CLOSURE DEVICE ASSEMBLY". Kupiecki et al describes a number ofdevices all which are said to be placed within the lumen of a feedvessel exterior to the aneurysm so to retain coils within the aneurysmcavity. That is to say that the retainer device is released in thevessel exterior to the aneurysm. The device is held in place via thepresence of radial pressure on the vessel wall. After the device isreleased and set in an appropriate place, a microcatheter is insertedinto the lumen behind the retainer device and the distal end of thecatheter is inserted into the aneurysm cavity. One or morevaso-occlusive devices is introduced into the aneurysm cavity. Theretainer device maintains the presence of those vaso-occlusive deviceswithin the aneurysm no matter whether the aneurysm is a large mouthaneurysm or not.

Another device for closing an aneurysm is found in U.S. Pat. No.5,749,894, to Engelson et al, for "ANEURYSM CLOSURE METHOD". In thisprocedure, a vaso-occlusive device such as a coil or braid has on itsouter surface a polymeric composition which may be reformed orsolidified in situ within the human body. The device is simply insertedinto the aneurysm and the polymer is then reformed, e.g., by theapplication of light, to melt or otherwise to reform the polymerexterior to the vaso-occlusive device. The vaso-occlusive device thensticks to itself at its various sites of contact and forms a rigid wholemass within the aneurysm.

There are a variety of other vaso-occlusive coils and devices which maybe specified herein. The material provided above is only exemplary ofthe patents and publications dealing with such devices. No coil retainerdevice of the structure described herein is seen in any of thereferences described above.

SUMMARY OF THE INVENTION

This invention includes an implantable medical device both, or either,useful for retaining other occlusion devices at an occlusion site, suchas an aneurysm, and at least partially closing the selected site byitself. The invention includes related methods of introducing andinstalling that medical device at the occlusion site. Combinations ofthe retainer device and its included vaso-occlusive material or deviceare also an aspect of the invention. In particular, the inventioninvolves an implantable retainer which is deliverable through anelongated tubular delivery device such as a vascular catheter. Theimplantable retainer may include a core wire having both a proximal endand a distal end. At the distal end is a joint which allows theinventive neck bridge to be disengaged from the core wire. The jointitself extends between the distal end of that core wire and a number ofarray elements. The joint may be of a type which is electrolyticallyseverable upon application of a suitable current to the joint. This typeof joint is comparatively more electrolytically dissolvable or erodiblein body fluids when a current is applied, than are any of the rest ofthe implantable retainer components. Finally the retainer assemblyitself has a number of array elements which are of a shape (a first ordelivery shape) which is deployable through a delivery catheter and,upon exit from the distal end of that catheter, readily assumes asecondary shape desirably conforming to the interior shape of theaneurysm catheter. Central to this invention is the use of arrayelements which vary in flexibility. The wires forming the array elementsmay differ in flexibility from array element to array element.

When using the preferred electrolytic joint, electrolysis of theseverable joint permits placement of the retainer assembly at theaneurysm and removal of the attached delivery apparatus. Placement ofthe vaso-occlusive device to be retained in the aneurysm may then be hadby simply introducing the vaso-occlusive device and its delivery tubularmember between the array elements in the aneurysm.

The array elements themselves may be loops or may be arms which simplyextend from the joint into the aneurysm cavity. It is within the scopeof this invention that the retainer assembly include a number of"exterior" array members which, in general, extend radially from theregion of the joint and are intended to remain in the feed vessel--notin the aneurysm--after deployment. These exterior loops define, with theinterior array elements an annular area between them into which the rimor mouth of the aneurysm may fit.

The various portions of the device may be made to be radio-opaque by thechoice of materials or by such other procedures as by wrapping thecomponents in a radio-opaque wire or ribbon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are respectively a side view and a top view of avariation of the inventive aneurysm retainers.

FIG. 2 is a top view of a variation of the inventive aneurysm retainer.

FIG. 3 is a top view of the inventive aneurysm retainer.

FIG. 4 is a partial side view of the inventive aneurysm retainer placedin an aneurysm.

FIGS. 5A and 5B show respectively a partial cross sectional side viewand top view of a variation of the inventive aneurysm retainer within ananeurysm.

FIGS. 6A to 6E show a method of deploying a device made according tothis invention and the vaso-occlusive devices therein.

DESCRIPTION OF THE INVENTION

This invention involves a device and procedure for solving both theproblems of closing aneurysm openings and of stabilizing the structureand placement of vaso-occlusive devices when they are placed in ananeurysm. These retaining devices generally are intended to prevent themigration of one or more occlusion devices such as coils from a targetocclusion site, by forming a barrier at the entrance zone to the targetsite from a feeding vessel. The remainder of the retainer device whichis remote from the mouth generally provides stability to the portion ofthe device which is in the mouth of the aneurysm.

FIGS. 1A and 1B show a most typical but simple variation of theinventive device (100). The retainer assembly (100) has a shape whichdesirably approximates that of the mouth of the aneurysm into which itis placed. Specifically, the retainer device (100) has a plurality ofarray elements (102, 104) which extend from the preferred electrolyticjoint (106) and form a loop which comes around to join itself back inthe vicinity of electrolytic joint (106). It is, of course, permissibleto use joints other than electrolytic joints in place of (106), e.g.,joints which rely upon mechanical joining for structural certainty.However, joint (106) is desirably electrolytically severable becausesuch joints are very functionally flexible in their deployment. That isto say, that should the aneurysm retainer somehow be malplaced, the factthat core wire (not shown) may be used to withdraw this device back intoits delivery catheter or other suitable delivery tubular member, is avery big benefit.

FIG. 1A, a side view of the inventive retainer (100), shows anotheraspect of this invention which is sometimes significant in use. In thisvariation, the various array members (102, 104) are indented from thepatent artery. This configuration has at least two benefits. First ofall, the joint itself is not placed in the feed artery and should notcause the creation of an embolus in that vessel with the danger ofsubsequent blockage. Furthermore, the plurality of array wires (as maybe shown from the top view in FIG. 1B) form what might be characterizedas a skeletal funnel at the top of the retainer device (100) andconsequently in the aneurysm itself, placement or re-placement of thefeed catheter in the retainer device so to permit introduction of thevaso-occlusive member (not shown) into the interior volume of theaneurysm retainer device is simplified.

This variation of the invention as well as the others discussed below,are delivered through a tubular member such as a catheter. The shape ofthe device shown in FIG. 1A is the so-called secondary shape found afterthe retainer device (100) has been pushed from the distal end of thedelivery device. The retainer device (100) generally has a relativelylinear shape as is pushed through catheter. This primary or deliveryshape is essentially the shape of the interior of the catheter duringthe delivery step. After deployment, the device assumes its secondaryshape as is seen in FIG. 1A.

To undergo such massive changes in shape, it is usually preferable thatthe interior array elements (102) be produced of material such as asuperelastic alloy. Superelastic or pseudoelastic shape recovery alloysare well known in this art. For instance, U.S. Pat. Nos. 3,174,851;3,351,463; and 3,753,700 each describe one of the more well knownsuperelastic alloys, also known generically as nitinol. These alloys arecharacterized by their ability to be transformed from an austeniticcrystal structure to a stress-induced-martensitic (SIM) structure atcertain temperatures and then return elastically to the austenitic shapewhen the stress is removed. These alternating crystal structures providethe alloy with its superelastic properties. The alloy mentioned in thethree patents just above, is a nickel-titanium alloy. It is readilycommercially available and undergoes the austenitic-SIM-austenitictransformation in a variety of temperatures between -20° C. and +30° C.

These alloys are especially suitable because of their capacity torecover elastically--almost completely--to the initial configurationonce the stress is removed. Typically, in these services, there islittle plastic deformation even at relatively high strains. This allowsthe retainer device (100) to undertake substantial bends both as it iscollapsed to enter the tubular delivery device and as it undertakesfurther bending in passing through turns in the vasculature. In spite ofthis bending, it returns to its original shape once the bend has beentraversed without retaining a kink or a bend.

Of the superelastic alloys currently available, we consider a preferredmaterial to be nominally 50.6±2% nickel and most of the remainder,titanium. Up to about 5% of the alloy may be another member of the irongroup of metals, particularly chromium and iron. The alloy shouldn'tcontain more than about 500 parts per million of oxygen, carbon, ornitrogen. The transition temperature of this material is notparticularly important, but it should be reasonably below the typicaltemperature of the human body so to allow it to be in its austiniticphase during use. The diameter of the wires or ribbons making up thearray elements preferably are smaller than about 0.010 inches indiameter. As will be discussed below, the typical superelastic alloy isnot always completely visible under fluoroscopy. Consequently, it isoften desirable to add some type of a covering to improve theradio-opacity of the device. Radio-opaque metals such as gold andplatinum are well known.

Although we have discussed the concept that these devices are desirablymade from superelastic alloys, other metals may in certain circumstancesbe appropriate. Such metals include a number of the stainless steels andother highly elastic, if not superelastic alloys. Furthermore, it iswithin the scope of this invention that the array elements (102, 104) beof polymeric material. Polymeric materials are somewhat easier to workwith in forming the device and may also suitable for maintaining thevaso-occlusive devices at an appropriate site within the aneurysm. Suchmaterials as polyethylene, polypropylene, polytetrafluoroethylene,various of the Nylons, and the like would be easily chosen by one havingordinary skill in this art for the purposes shown herein.

Central to the invention is the use of array elements, or theirconstituent wires or ribbons, which differ in flexibility. That is tosay that in the variation shown in FIGS. 1A and 1B, the axial arrayelements (104) may less stiff (more flexible) than the circumferentialarray elements (102). This variation provides for a stabilization of theinventive neck bridge (100) due to the relatively firmer pressure placedon the neck by the circumferential array elements (102) and the softer,but more widely spread, pressure from the axial array elements (104).

Although it is quite desirable from the perspective of the physicianuser to have a device which is symmetrical in providing pressuredistally and proximally on the aneurysm and side to side as well, suchis not absolutely necessary. Opposing pairs of array members having thesame flexibility or composed of constituent wires or ribbons having thesame flexibility are highly desired but not always necessary dependingupon the situation.

Although the array elements (102, 104) are generally shown to be regularand of the approximate same shape on each of the axes through theretainer device (100), such obviously need not be the case. It is withinthe scope of this invention that the retainer assembly be irregular inshape so to fit the shape of an irregular aneurysm. Placement of suchdevices must be done with some care, but it is within the purview of onehaving ordinary skill in the art with some instruction.

FIG. 2 shows another variation of the inventive retainer assembly (110)in which the circumferential array elements (110) are multiple. Axialarray element (112) is of the same general shape as those shown in FIG.1A and FIG. 1B. These circumferentially extending loops (112) areintended to fit within the aneurysm and provide lateral stability to theplacement of the retainer device (110). A pair of axial array elements(114) is shown in FIG. 2. The invention is, obviously, not so limited.

The generally circumferential array elements (112) may have larger loopsthan those shown in the Figure. Again, this device is desirably situatedin its secondary form so that the remainder of any attachment element,attached formerly joint (116) after separation from the feed or corewire, will not extend into the feeder vessel for this aneurysm. Thisretainer assembly (110) may be used to help close an aneurysm which isof substantial length but nominal width.

Again, it is desirable that the circumferential array elements (112) beof a different flexibility than the axial array elements (114) or beconstructed of wires or ribbons having differing flexibilities.

FIG. 3 shows still another variation of the inventive device (140). Thisvariation shows multiple array members of varying size (142, 144, 146)attached to a generally central detachment joint (148), which joint maybe of a design such as those discussed above.

Although the overall configuration of this device (140) as shown in FIG.3 may be indented at the top in the same manner as the variations shownin FIG. 1B, this neck configuration is shown for purposes of completingthe variations of this invention. The array members (142, 144, 146) to acore wire (as shown below) via a ferrule (150) perhaps by crimping orperhaps by welding the devices components together.

FIG. 4 shows the placement of an inventive device (160) in awide-mouthed aneurysm (162). this neck bridge (160) lacks the detent atthe joint shown in the variations above. However, the core or deliverywire (166) attached to the detachable joint (164) is shown. It should benoted that the axial array members (168) lay along the aneurysm wall andthe circumferential members (170) are generally across the mouth of theaneurysm. In most instances, the back wall of the aneurysm is especiallyweak and the neck of the aneurysm is considered to be the strongestretention point.

FIGS. 5A and 5B show the placement of the variation (160) of theinventive device in a narrow neck aneurysm. FIG. 5A is a cross-sectionand FIG. 5B is a top-view cross section centering on the aneurysm mouthas viewed from mid-artery. Again, this shows the axial or longitudinalarray members (168) extending in a direction along the axis of theartery and the circumferential array members (170) extending around aportion of the circumference of the aneurysm generally, in this case,orthogonal to the axis of the artery axis. Finally, the aneurysm isshown having a vaso-occlusive device, in this instance a helical coil,in the volume of the aneurysm (180).

This device may be deployed in the following manner. FIG. 6A shows aberry aneurysm (200) emanating from the wall of an artery (202). Acatheter (204) is shown having radio-opaque band (206) at its distalend. The distal end of catheter (204) extends into the mouth (208) ofthe aneurysm (200). FIG. 6B shows a retainer device (212) having a shapesimilar to those discussed above. This variation of the inventiveretainer (212) has circumferential array members (214) and axial arraymembers (216). It should probably be apparent that the various arraymembers should not pinch the aneurysm in any very meaningful ordeleterious way, lest some type of rupture occur.

In FIG. 6C, it can be seen that the voltage has been applied to corewire (218), and the electrolytic joint has been dissolved. The core wire(218) is then withdrawn from catheter (204) and discarded. It may bealso seen in FIG. 6C that the region of the joint adjacent the retainerdevice (212) is recessed out of the flow of artery (202).

The electrolytic severable joint may also be called a sacrificial link.Core wire (210) is typically coated with an electrical insulator whichis not susceptible to dissolution via electrolysis in blood or otherionic media. Suitable coatings for core wire (210) include suchinsulating materials as the polyfluorocarbons (e.g., Teflon),polyurethane, polyethylene, polypropylene, polyimides or other suitablepolymeric materials. The sacrificial joint is not coated with such aninsulator and is of a material which is susceptible to electrolyticdissolution in blood. The sacificial joint may be a simple un-insulatedcontinuation of, e.g., stainless steel core wire (210), which has beeninsulated proximally of the joint. It should also be apparent that thesacrificial joint is more susceptible to electrolysis than are the arrayelements. Further discussion of construction of, placement of, and otherphysical details of such a joint may be found in U.S. Pat. Nos.5,122,136 to Guglielmi et al.; 5,354,295 to Guglielmi et al.; 5,624,449,to Pham et al., and others.

In FIG. 6D, catheter (204) has been re-introduced into the neck ofaneurysm (200) and a number of vaso-occlusive devices--in this case,coils (220)--have been introduced into the volume formed by retainerassembly (212).

FIG. 6E show the withdrawal of catheter (204) from the feed vessel withthe implantation of vaso-occlusive coils (220) and their stabilizingretainer (212) complete.

Many alterations and modifications may be made by those of ordinaryskill in this art, without departing from the spirit and scope of thisinvention. The illustrated embodiments have been shown on for purposesof clarity and the example should not be taken as limiting the inventionas defined in the following claims, which are intended to include allequivalents, whether now or later devised.

We claim:
 1. An implantable retainer bridge, deliverable via an elongatetubular delivery device, of a size and overall flexibility to safelylodge at the mouth of a vascular aneurysm, and suitable for retaining atleast a vaso-occlusive device in a vascular aneurysm, comprising:a) adetachable joint located centrally to a plurality of array elements, anddetachable from a core wire delivery element, and b) said plurality ofarray elements extending outwardly from and fixedly attached to saiddetachable joint, wherein said plurality of array elements is comprisedof at least two array pairs, each such array pair elements extendingfrom said detachable joint in an opposing direction, is comprised oflooped wires extending from and looping back to said detachable joint,and wherein at least one array pair element wire is more flexible thananother said at least one array pair element.
 2. The implantableretainer bridge of claim 1, wherein said detachable joint comprises anelectrolytically severable joint suitable for separating said core wiredelivery element from said implantable retainer upon application of asuitable current to said joint, said joint being comparatively moresusceptible to electrolytic severability than said core wire deliveryelement and said plurality of array elements.
 3. The implantableretainer bridge of claim 1, wherein said detachable joint comprises amechanically detachable joint suitable for separating said core wiredelivery element from said implantable retainer.
 4. The implantableretainer bridge of claim 1, wherein said implantable retainer has afirst delivery shape when retained within said elongate tubular deliverydevice and having a distal delivery end and a proximal delivery end, anda second deployed shape, different than first delivery shape, when saidimplantable retainer is not retained within said tubular delivery deviceand having a distal deployed and an proximal deployed end, saidplurality of array elements extends outwardly from said joint in saidsecond deployed shape.
 5. The implantable retainer bridge of claim 2further comprising a core wire delivery element, wherein said core wiredelivery element is covered with an electrical insulation layer fromnear its proximal end to near its distal end.
 6. The implantableretainer bridge of claim 1, wherein said plurality of array elementscomprise platinum.
 7. The implantable retainer bridge of claim 1 whereinsaid plurality of array elements comprise tantalum.
 8. The implantableretainer bridge of claim 1 wherein said plurality of array elementscomprise stainless steel.
 9. The implantable retainer bridge of claim 1wherein said plurality of array elements comprise a super-elastic alloy.10. The implantable retainer bridge of claim 1 wherein at least aportion of said plurality of array elements is covered by radio-opaquematerial.
 11. The implantable retainer bridge of claim 10 wherein saidradio-opaque material is platinum.